Scientists studying yo-yo dieting in mice say the tendency for people to regain excess weight rapidly after successfully slimming may well be due to their microbiome - the trillions of microorganisms in the gut.
The researchers, from the Weizmann Institute of Science in Israel, found that changes in the gut microbiome that occur when an obese mouse loses weight can persist for many months, and that this contributes to accelerated weight regain later if the diet lapses.
If, as the researchers believe, a similar thing happens in obese people, they said, it could help explain why so many of them fail to keep their lost weight off, and often put on more than they lost in the first place.
According to the scientists, up to 50 percent of obese people suffer this relapsing pattern of weight loss and regain.
To try to find out why, the they experimented with mice, giving them cycles of high fat diets interspersed with periods of lower-fat normal diet.
Microbiome + diet changes cause weight regain
They found that the gut microbiomes of the mice who lost weight were altered, and that these changes remained in place for many months and contributed to rapid and excessive weight gain if the mice were given high-fat diets again.
To test whether it was due to the microbiome, the researchers transferred the altered microbiomes into mice that had not previously been exposed to yo-yo diets - and here too they found unusually rapid and excessive weight gain when the mice were given high-fat foods. "The microbiome by itself is not sufficient to produce rapid weight again); it's the diet plus the microbiome, the researchers explained.
Lack of flavonoids may be involved
The scientists were not able to say exactly what the mechanism is or how exactly the microbiome's persistent post-diet state increases weight gain.
In a further analysis of the microbiome, they found that among key changes were a reduction in levels of plant compounds called flavonoids in the gut after dieting, and reduced energy expenditure.
Flavonoids are bioactive compounds found in fruits, vegetables, legumes, tea, chocolate and red wine. The 4,000-plus different flavonoids found in foods can be divided into subclasses; the ones we most commonly consume include anthocyanins (e.g., berries, plum, red grapes), flavonols (e.g., onion, kale, broccoli), flavones (e.g., Parsley, thyme, celery, chili peppers) and flavonones (e.g., oranges, grapefruit, lemons).
This suggests, they said, that a flavonoid-based "post-biotic" treatment might help curb post-dieting weight regain.
The team has now started work on exploring whether human gut microbiomes respond in a similar way to those in mice, and whether treatments could be developed to restore the microbiome more swiftly to its regular state after dieting.
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